As a measuring apparatus for detecting the transmission loss characteristic of an optical fiber or its connected portion for detecting a deteriorated portion such as a fractured point, an optical fiber measuring apparatus is known which uses a so-called optical time-domain reflector (OTDR) in which measurement is effected by detecting its backscattered light and reflected light.
Conventionally, the optical fiber measuring apparatus such as the one described above includes an optical pulse generating source for generating predetermined optical pulses which are made incident upon an optical fiber subject to measurement. The optical pulse generating source is a light source such as a laser for generating optical pulses of a predetermined wavelength and is repeatedly driven at predetermined timings to generate optical pulses at predetermined intervals. The optical pulses which are repeatedly generated from the light source are made incident from one end of the optical fiber subject to measurement through an optical pulse input/output circuit such as an optical directional coupler. The return light is detected by a light receiver such as a photodiode through the optical directional coupler. The detected return light is converted into an electrical signal and outputted by the photodiode, is amplified by an amplifier, and is supplied to a signal processing circuit. The signal processing circuit effects sampling with respect to the signal of the return light, which is converted into the electrical signal and amplified, at predetermined timings corresponding to the repetition timing at the optical pulse generating source. The sampled signals are averaged in correspondence with the number of repetition of the optical pulses, and a loss characteristic corresponding to that signal level is determined. Further, the results of processing are subjected to, for example, logarithmic conversion, and a rightwardly descending loss waveform is formed, the waveform being displayed on a display section.
However, with the above-described conventional technique, when the return light of a plurality of different wavelengths scattered or reflected in the optical fiber is measured, the return light of a wavelength to be measured is detected by effecting a changeover in an optical pulse input/output circuit, and measurement must be effected for each wavelength. Therefore, there have been problems in that it takes time in measuring all the return light of the plurality of wavelengths to be measured, and time and trouble are involved in its changeover operation. Accordingly, an arrangement is conceivable in which the return light is outputted by being divided into a plurality of wavelengths through a filter or the like, the respective return light is detected by a plurality of detecting circuits, and signal processing is effected at a time by a plurality of signal processing circuits. In this case, however, since the speed of light advancing in the optical fiber differs depending on the wavelength, in the case of the return light of different wavelengths detected simultaneously, signals in which the reflected position in the optical fiber, i.e., the distance from a detecting end, differs are detected and processed. Therefore, there arises the problem that accurate comparison of data obtained from those results becomes difficult in some cases.